Recently, the importance of the addition of polyunsaturated fatty acids (PUFA's) to infant formulas has been acknowledged (see for instance U.S. Pat. No. 4,670,285 and European Patent Publications EP-A-0231904 and EP-A-0404058).
Infant formula is usually prepared by the following general process.
1. Pasteurised milk (skimmed, evaporated or whole milk) is standardised by the addition of whey protein concentrate, minerals, water-soluble vitamins, trace elements and carbohydrates at high temperatures, for example 60.degree. C.
2. Vegetable oil, oil-soluble emulsifiers, oil-soluble vitamins and anti-oxidants are mixed at high temperatures, for example 60.degree. C.
3. The oil mixture obtained from 2 (an oil phase) is added to the standardised milk obtained from 1 (a water phase) with sufficient agitation to allow mixing.
4. The mixture obtained in 3 is homogenised in two stages at high temperature and pressure, for example 60.degree. C. at 150 and 30 bar.
5. The emulsion obtained under 4 is cooled to a low temperature, for example 5.degree. C.
6. If desired, water-soluble vitamins, minerals and trace elements are added to the cooled emulsion.
7a. Emulsion 6 is sterilised on-line at ultra high temperature (UHT) and/or in appropriate containers to obtain a formula in the form of a sterile liquid; or
7b. Emulsion 6 is pasteurised and spray dried to give a spray dried powder which is filled into appropriate containers.
8. If desired, other dry ingredients, e.g. vitamins, minerals, trace elements, whey protein concentrate and carbohydrates can be added to the spray dried powder from 7b.
Thus at several points in the infant formula preparation process high temperatures and pressures are used, for example during the following process steps:
melting and blending fats in the oil phase (2) ; PA1 dissolving oil soluble emulsifiers in the oil phase before homogenisation (2); PA1 pasteurisation before homogenisation (in 4); PA1 homogenisation (4); PA1 sterilisation (7a); PA1 pasteurisation after homogenisation (7b); and/or PA1 spray drying, if performed (7b).
Typically, the PUFA 's which are used for the supplementation of infant formula are in a triglyceride, phospholipid, fatty acid or fatty acid ester form and are oily liquids. The most convenient way to disperse PUFA-containing lipids homogeneously is by mixing them in with the oil phase before the homogenisation step. Thus, currently, the PUFA-containing lipid is added to the oil phase, because the PUFAs are usually contained in lipids which themselves are oils. This is much easier than trying to homogeneously disperse the PUFAs in the formula at a later stage, especially once the emulsion in (3) has been formed.
International patent application WO-A-94/01001 refers to the necessity of protecting PUFA-containing lipids from substances which attack the double bonds. It describes a microencapsulation process for PUFA-containing lipids, by providing these lipids in a free flowing powdered form to be readily mixed with other dry or liquid components.